Various techniques such as a technique using a reference light and a stereo ranging technique using a plurality of cameras are known as imaging techniques for obtaining a depth-direction distance to a subject, serving as two-dimensional array information. In particular, in recent years, imaging devices capable of obtaining distance information at relatively low costs have been increasingly needed to serve as newly developed consumer input devices.
In order to meet the needs, an imaging device with an imaging lens and a compound eye structure is proposed, which obtains multiple parallaxes with the compound eye structure, and is capable of preventing the resolution from being lowered. The imaging device includes, for example, an imaging lens, and a plurality of optical systems serving as re-imaging optical systems arranged between the imaging lens and an imaging element. For example, a microlens array including a plurality of microlenses arranged on a flat substrate is used as the optical systems. Pixels are arranged below the microlenses, each on a position corresponding to a microlens, to obtain images of the microlenses. An image formed by the imaging lens is re-imaged on the imaging element by means of the re-imaging microlenses. The viewpoint of each single-eye image that is re-imaged is shifted from that of an adjacent image by the parallax caused by the position of the corresponding microlens.
A distance to a subject can be estimated based on the principle of triangulation by image-processing the parallax images obtained from the microlenses. Furthermore, the parallax images can be re-configured as a two-dimensional image by combining them by image-processing.
However, the pixels in the aforementioned compound-eye imaging device are reduced by the image-processing. For this reason, a function is needed to switch an imaging mode for obtaining a distance to a subject in a depth direction and an imaging mode for obtaining a high-resolution two-dimensional image.
Liquid crystal optical elements using sealed liquid crystal or gradient index lens (GRIN) are known to have a switching function. The sealed type liquid crystal optical element has an electrode having a concave lens shape, and an alignment film is formed and liquid crystal is filled in the concave portion. In this case, a problem arises in that the alignment film cannot be easily formed uniformly, and the refractive index of the liquid crystal cannot be made uniform easily. On the other hand, with respect to the GRIN type, a hemiprism (lenticular) lens can be formed easily, but a two-dimensional lens array cannot be formed easily.